U.S. patent number 9,044,947 [Application Number 13/483,417] was granted by the patent office on 2015-06-02 for ink jet printing apparatus and ink jet printing method.
This patent grant is currently assigned to CANON KABUSHIKI KAISHA. The grantee listed for this patent is Makoto Akahira, Satoshi Wada, Hiromitsu Yamaguchi. Invention is credited to Makoto Akahira, Satoshi Wada, Hiromitsu Yamaguchi.
United States Patent |
9,044,947 |
Wada , et al. |
June 2, 2015 |
Ink jet printing apparatus and ink jet printing method
Abstract
An object of the present invention is to provide an ink jet
printing apparatus which can prevent possible stripe-like density
unevenness in a joint in a print head constructed by joining a
plurality of chips together even if the print head is inclined to
the regular position of the print head. The present invention uses
a print head having the nozzle arrays being shifted in a direction
in which the nozzles are arranged, so as to have overlapping
portions in a direction orthogonal to the nozzle arranging
direction. The present invention controls an ink ejecting operation
of the nozzles in the overlapping portions between the plurality of
nozzle arrays on the basis of an angle between the nozzle array
arranging direction and a direction orthogonal to the direction in
which the print head moves relative to the print medium.
Inventors: |
Wada; Satoshi (Machida,
JP), Yamaguchi; Hiromitsu (Yokohama, JP),
Akahira; Makoto (Yokohama, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Wada; Satoshi
Yamaguchi; Hiromitsu
Akahira; Makoto |
Machida
Yokohama
Yokohama |
N/A
N/A
N/A |
JP
JP
JP |
|
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Assignee: |
CANON KABUSHIKI KAISHA (Tokyo,
JP)
|
Family
ID: |
39840973 |
Appl.
No.: |
13/483,417 |
Filed: |
May 30, 2012 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20120236055 A1 |
Sep 20, 2012 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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12024628 |
Feb 1, 2008 |
8210638 |
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Foreign Application Priority Data
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Feb 14, 2007 [JP] |
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2007-033650 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B41J
2/04541 (20130101); B41J 2/155 (20130101); B41J
2/04588 (20130101); B41J 2/2132 (20130101); B41J
2/04598 (20130101); B41J 2/0458 (20130101); B41J
2/04505 (20130101); B41J 29/393 (20130101); B41J
2202/20 (20130101) |
Current International
Class: |
B41J
29/393 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Seo; Justin
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper &
Scinto
Parent Case Text
This application is a continuation of application Ser. No.
12/024,628, now allowed.
Claims
What is claimed is:
1. An ink jet printing apparatus comprising: a conveyance unit
configured to convey a print medium in a first direction; a print
head unit configured to print on the print medium, the print head
unit comprising a first print head chip that includes a first
nozzle array formed by first nozzles, and a second print head chip
that includes a second nozzle array formed by second nozzles, the
first print head chip and the second print head chip being arrayed
in a second direction crossing the first direction such that the
first nozzles in the first print head chip and the second nozzles
in the second print head chip print two adjacent lines,
respectively, each of which is printed in a direction crossing the
second direction; and a controller configured to control ejection
of ink by the first nozzles and the second nozzles according to an
angle between a longitudinal direction of the print head unit and
the first direction.
2. The ink jet printing apparatus according to claim 1, wherein the
first nozzles in the first print head chip and the second nozzles
in the second print head chip print different lines in the
direction crossing the second direction.
3. The ink jet printing apparatus according to claim 1, wherein a
position of the first print head chip in the first direction is
different from a position of the second print head chip in the
first direction.
4. The ink jet printing apparatus according to claim 1, wherein the
print head unit further comprises a retrieval unit configured to
retrieve information regarding the angle between the longitudinal
direction of the print head unit and the first direction, wherein
the controller controls ejection of ink by the first nozzles and
the second nozzles based on the information retrieved by the
retrieval unit.
5. The ink jet printing apparatus according to claim 1, wherein the
controller controls a number of ink drops ejected from the first
nozzles or the second nozzles.
6. The ink jet printing apparatus according to claim 1, wherein the
first print head chip and the second print head chip are each
provided with a plurality of nozzle arrays.
7. The ink jet printing apparatus according to claim 6, wherein in
each of the first print head chip and the second print head chip,
nozzles of one of the plurality of nozzle arrays are arrayed so as
to be shifted from nozzles of another one of the plurality of
nozzle arrays by a distance less than a nozzle arranging pitch.
8. An ink jet printing method comprising: a conveyance step of
conveying a print medium in a first direction; a printing step of
printing on the print medium with a print head unit comprising (i)
a first print head chip that includes a first nozzle array formed
by first nozzles and (ii) a second print head chip that includes a
second nozzle array formed by second nozzles, wherein the first
print head chip and the second print head chip are arrayed in a
second direction crossing the first direction such that the first
nozzles and the second nozzles print two adjacent lines,
respectively, in a direction crossing the second direction; and a
control step of controlling ink ejection by the first nozzles and
the second nozzles according to an angle between a longitudinal
direction of the print head unit and the first direction.
9. The ink jet printing method according to claim 8, wherein the
nozzles in the first print head chip and the nozzles in the second
print head chip print different lines in the direction crossing to
the second direction.
10. The ink jet printing method according to claim 8, wherein a
position of the first print head chip in the first direction is
different from a position of the second print head chip in the
first direction.
11. The ink jet printing method according to claim 8, further
comprising: a retrieval step of retrieving information regarding
the angle between the longitudinal direction of the print head unit
and the first direction, wherein the control step includes
controlling ink ejection by the first nozzles and the second
nozzles based on the retrieved information.
12. The ink jet printing method according to claim 8, wherein a
number of ink drops ejected from the first nozzles or the second
nozzles is controlled in the control step.
13. The ink jet printing method according to claim 8, wherein the
first print head chip and the second print head chip are each
provided with a plurality of nozzle arrays.
14. The ink jet printing method according to claim 13, wherein in
each of the first print head chip and the second print head chip,
nozzles of one of the plurality of nozzle arrays are arrayed so as
to be shifted from nozzles of another one of the plurality of
nozzle arrays by a distance less than a nozzle arranging pitch.
15. A printing controlling apparatus for controlling printing on a
print medium, conveyed in a first direction, by a print head unit
which is configured to print on the print medium, the print head
unit including: a first print head chip, that includes a first
nozzle array formed by first nozzles, and a second print head chip,
that includes a second nozzle array formed by second nozzles, the
first nozzles and the second nozzles being arrayed in a second
direction crossing to the first direction, the printing controlling
apparatus comprising: a print performing unit configured to perform
printing such that the first nozzles in the first print head chip
and the second nozzles in the second print head chip print two
adjacent lines, respectively, in a direction crossing to the second
direction; and a controller configured to control ink ejection by
the first nozzles and the second nozzles according to an angle
between a longitudinal direction of the print head unit and the
first direction.
16. The printing controlling apparatus according to claim 15,
wherein the first nozzles in the first print head chip and the
second nozzles in the second print head chip print different lines
in a direction crossing the second direction.
17. The printing controlling apparatus according to claim 15,
wherein a position of the first print head chip in the first
direction is different from a position of the second print head
chip in the first direction.
18. The printing controlling apparatus according to claim 15,
wherein the controller controls a number of ink drops ejected from
the first nozzles or the second nozzles.
19. The printing controlling apparatus according to claim 15,
wherein the first print head chip and the second print head chip
are each provided with a plurality of the nozzle arrays.
20. The printing controlling apparatus according to claim 19,
wherein in each of the first print head chip and the second print
head chip, nozzles of one of the plurality of nozzle arrays are
arrayed so as to be shifted from nozzles of another one of the
plurality of nozzle arrays by a distance less than a nozzle
arranging pitch.
21. An ink jet printing apparatus comprising: a conveyance unit
configured to convey a print medium in a first direction; a print
head unit configured to print on the print medium, the print head
unit comprising a plurality of print head chips for the same color,
each of which includes a nozzle array formed by a plurality of
nozzles, the plurality of print head chips being arrayed in a
second direction crossing the first direction such that respective
end nozzles of nozzle arrays used for printing corresponding to two
adjacent print head chips of the plurality of print head chips are
adjacent to each other in the second direction; an obtaining unit
configured to obtain information on a shift amount of printing
positions by respective nozzles in the print head unit in the first
direction; and a controller configured to control ejection of ink
by at least one nozzle of the respective end nozzles in the two
adjacent print head chips of the plurality of print head chips
based on the information on the shift amount, wherein the
controller controls a number of ink drops ejected from at least one
nozzle of the respective end nozzles based on the information on
the shift amount.
22. The ink jet printing apparatus according to claim 21, wherein a
position of a first print head chip of the plurality of print head
chips in the first direction is different from a position of a
second print head chip of the plurality of print head chips in the
first direction.
23. The ink jet printing apparatus according to claim 21, wherein
the print head unit prints a pattern for obtaining the information
and the obtaining unit obtains the information based on the
pattern.
24. The ink jet printing apparatus according to claim 23, wherein
the print head unit is further configured to print a first pattern
using a nozzle in one end chip of the plurality of print head chips
in the second direction and print a second pattern using another
nozzle in another end chip of the plurality of print head chips in
the second direction in order to print the pattern.
25. The ink jet printing apparatus according to claim 21, wherein
the plurality of print head chips are each provided with a
plurality of nozzle arrays.
26. The ink jet printing apparatus according to claim 21, further
comprising an optical sensor configured to measure a printed
pattern.
27. The ink jet printing apparatus according to claim 21, wherein
the controller controls a volume of an ink drop ejected from at
least one nozzle of the respective end nozzles based on the
information on the shift amount.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet printing apparatus that
prints an image on a print medium by ejecting ink onto the print
medium through nozzles formed in a print head, and in particular,
to a printing apparatus using a print head having a plurality of
relatively short chips which are arranged to increase the length of
the print head and in each of which nozzles are arranged.
2. Description of the Related Art
Advantageously, ink jet printing apparatuses generate only low
noise during printing because the apparatuses cause ink droplets to
land on a print medium for printing. The ink jet printing apparatus
also requires only low running costs owing to its capability of
printing ordinary paper and the like without any special process.
Furthermore, with the ink jet printing apparatus, using a plurality
of color inks enable color images to be relatively easily formed.
Moreover, densely arranging nozzles advantageously allows
high-resolution images to be formed at a high speed. In particular,
what is called a full-line printing apparatus is suitable for
increasing the speed of the image forming operation; the full-line
printing apparatus uses a long print head having a large number of
nozzles arranged in a direction orthogonal to a direction in which
print media are conveyed. The full-line printing apparatus may thus
be used as an on-demand printing apparatus, the need for which is
increasing. Accordingly, the full-line printing apparatus is thus
gathering much attention.
The on-demand printing is expected to save labor instead of
printing as much as several million copies as in the conventional
printing of newspapers or magazines or performing printing at a
very high speed, for example, printing one hundred thousand copies
per hour. The full-line printing apparatus offers a lower print
speed than conventional printers for offset printing or the like
but eliminates the need to make printing plates, making it possible
to save labor. The full-line printing apparatus further allows a
wide variety of print matter in small quantities to be printed in a
short time. Thus, the full-line printing apparatus is optimum for
on-demand printing.
The full-line printing apparatus used for the on-demand printing is
desired to print large-sized print media at a high resolution and a
high speed. For example, the full-line printing apparatus needs to
print at least 30 A3-sized print media per minute at a resolution
of at least 600.times.600 dpi for monochromatic documents
containing texts or the like or at a resolution of at least
1,200.times.1,200 dpi for full color images such as
photographs.
The full-line ink jet printing apparatus is not only desired to
print such large-sized print media but may also be used to print
images taken with a digital camera or the like on L-sized media as
in the case of conventional silver halide photography or on small
print media such as postcards.
The full-line ink jet printing apparatus thus has excellent
functions of dealing with print media of plural sizes and
performing printing at a high speed. Accordingly, the full-line ink
jet printing apparatus is expected to be widely used not only for
business use but also for domestic use.
However, for the full-line printing apparatus, it is very difficult
to form nozzles made up of ejection orifices, ink paths, or
ejection energy generating elements, over a wide range equal to or
greater than the print width of large-sized print medium without
causing any defect. For example, a printing apparatus providing
photographic outputs to large-sized sheets such as materials used
in offices or the like needs about 14,000 ejection orifices (print
width: about 280 mm) in order to print A3-sized print sheets at a
high density of 1,200 dpi. It is very difficult to provide ejection
energy generating elements corresponding to such a large number of
ejection orifices without causing any defect, in connection with a
manufacturing process. Thus, even if such nozzles can be
manufactured, efficiency percentage is low and enormous
manufacturing costs are required.
Thus, the full-line printing apparatus also uses a print head H
such as the one shown in FIG. 1. The print head H is what is called
a joint head formed by arranging a plurality of relatively short,
inexpensive chips CH such as those used in serial printing
apparatuses so that the chips are sequentially joined together to
form an elongate head as shown in FIGS. 1 and 2.
In the joint head H, the plurality of chips CH are arranged along
one direction. The chips CH located adjacent to each other in the
chip arranging direction are shifted in the chip arranging
direction and in a direction orthogonal to the chip arranging
direction. The chips CH located adjacent to each other in the chip
arranging direction have an overlapping portion (a joint portion or
an overlapping portion).
However, with the joint head H, a print image is likely to be
degraded in portions thereof corresponding to joints b and c of the
joint head H owing to the configuration thereof. Specifically, the
image is degraded if the direction in which the nozzles in the
joint head H, shown in FIGS. 1 and 2, are arranged is inclined at a
certain angle .theta. to a direction S orthogonal to a direction in
which the print head H performs a scan operation relative to a
print medium (with a full line head, a direction in which the print
medium is conveyed). That is, if the print head is inclined as
shown in FIG. 3, nozzle intervals in the head denoted by A, B, and
C have values expressed by Formulae 1, 2, and 3. In the formulae, R
denotes an inter-nozzle distance in the chips, Y denotes an
inter-joint-chip distance, and .theta. (.degree.) denotes the
inclination of the joint head H. Nozzle interval A:
R.times.COS(.theta.) (Formula 1) Nozzle interval B: (R+Y.times.TAN
(.theta.)).times.COS (.theta.) (Formula 2) Nozzle interval C:
(R-Y.times.TAN (.theta.)).times.COS (.theta.) (Formula 3)
Specifically, determination may be made, as described below, of by
what amount the nozzle intervals A, B, and C deviate from an
inter-nozzle distance R (the nozzle interval obtained when the
print head is located along the reference direction S (the
inclination is 0.degree.) if the print head is located under
conditions described below.
It is assumed that the nozzles in the head shown in FIGS. 1 and 2
have a density of 600 dpi, and
inter-nozzle distance: R=42.3 .mu.m,
inter-chip distance: Y=10 mm (=10,000 .mu.m), and
head inclination: .theta.=0.05.degree.. Then, the values of the
nozzle intervals A, B, and C are determined in accordance with the
formulae shown above. Then, the values obtained are compared with
the inter-nozzle distance (R=42. 3 .mu.m).
Distance A: 42. 29.mu. (almost no change)
Distance B: 51. 03.mu. (an increase of 8. 73 .mu.m)
Distance C: 33. 57.mu. (a decrease of 8. 73 .mu.m)
FIG. 19A shows a joint b including combinations (b1-b2) of nozzles
having the nozzle interval B, shown in FIG. 3, and combinations
(c1-c2) of nozzles having the nozzle interval C, shown in FIG. 3.
As shown in FIG. 19A, in the joint b, four types of combinations
(b1-b2) are possible for the nozzles having the nozzle interval B.
Two types of combinations (c1-c2) are possible for the nozzles
having the nozzle interval C. That is, in the joint b, the number
of combinations (b1-b2) of the nozzles having the nozzle interval B
is greater than that of combinations (c1-c2) of the nozzles having
the nozzle interval C. Consequently, in the joint b, the number of
areas printed by the nozzles having the nozzle interval B is larger
than that of areas printed by the nozzles having the nozzle
interval C.
FIG. 19B is a diagram showing an example of arrangement of dots
printed by nozzles located in the joint b and the vicinity of the
joint b when the print head H is tilted. In FIG. 19B, black circles
denote dots printed by nozzles in a chip CH (N). White circles
denote dots printed by nozzles in a CH (N-1). A method of printing
dots corresponding to the joint b using the joint head H involves
printing the dots so that the dots printed by the nozzles in the
chip CH(N) alternate with the dots printed by the nozzles in the
chip CH (N-1) array by array as shown in the figure.
In FIG. 19B, dots having a dot interval B' are printed by the
nozzles having the nozzle interval B. The other dots are printed by
nozzles in the same chip, that is, the nozzles having the nozzle
interval A. The nozzle interval A is almost equal to the nozzle
interval R, corresponding to the non-tilted print head. Thus, the
dots printed by the nozzles having the nozzle interval A are
uniformly arranged. However, since the nozzle interval B is greater
than the nozzle interval R, a blank is formed between the dots
printed by the nozzles having the nozzle interval B, that is, the
dots having the dot interval B'. This causes the vicinity of the
joint b to be perceived as a white stripe.
FIG. 19C is a diagram showing another example of arrangement of the
dots printed using the nozzles arranged in the joint b and the
vicinity of the joint b. The method of printing the dots
corresponding to the joint b differs between FIGS. 19B and 19C. In
FIG. 19C, in the joint b, the dots printed by the nozzles in the
chip CH(N) are staggered with respect to the dots printed by the
nozzles in the chip CH(N-1).
In FIG. 19C, dots having a dot interval B' are printed by the
nozzles having the nozzle interval B. Dots having a dot interval C'
are printed by the nozzles having the nozzle interval C. The other
dots are printed by nozzles in the same chip, that is, the nozzles
having the nozzle interval A. In FIG. 19C, some of the dots are
printed by the nozzles having the nozzle interval C, which is
smaller than the nozzle interval R, corresponding to the non-tilted
print head. However, as shown in FIG. 19A, in the joint b, the
number of combinations (b1-b2) of the nozzles having the nozzle
interval B is larger than that of combinations of the nozzles
having the nozzle interval C. Consequently, in the joint b, the
number of dots having the dot interval B' is larger than that of
dots having a dot interval C'. An area printed by the nozzles
located in the joint b and the vicinity of the joint b is thus
perceived as a white stripe.
FIG. 20A shows a joint c including combinations (b1-b2) of the
nozzles having the nozzle interval B, shown in FIG. 3, and
combinations (c1-c2) of the nozzles having the nozzle interval C,
shown in FIG. 3. As shown in FIG. 20A, in the joint c, two types of
combinations (b1-b2) are possible for the nozzles having the nozzle
interval B. Four types of combinations (c1-c2) are possible for the
nozzles having the nozzle interval C. That is, in the joint c, the
number of combinations (c1-c2) of the nozzles having the nozzle
interval C is larger than that of combinations (b1-b2) of the
nozzles having the nozzle interval B. Consequently, in the joint c,
the number of areas printed by the nozzles having the nozzle
interval C is greater than that of areas printed by the nozzles
having the nozzle interval B.
FIGS. 20B and 20C show the arrangement of dots printed by nozzles
located in the vicinity of the joint c and the vicinity of the
joint c when the print head H is tilted. Black circles denote dots
printed by nozzles in a chip CH(N). White circles denote dots
printed by nozzles in a CH(N+1). A method of printing dots
corresponding to the joint c as shown in FIGS. 20B and 20C is the
same as the method of printing dots corresponding to the joint b as
shown in FIGS. 19B and 19C.
In FIG. 20B, dots overlap each other which are printed by the
nozzles having the nozzle interval B, which is smaller than the
nozzle interval R, corresponding to the non-tilted print head H. An
area printed by the nozzles located in the joint c and the vicinity
of the joint c is thus perceived as a black stripe.
In FIG. 20C, some of the dots are printed by the nozzles having the
nozzle interval B, which is larger than the nozzle interval R,
corresponding to the non-tilted print head. However, as shown in
FIG. 20A, in the joint c, the number of combinations (c1-c2) of the
nozzles having the nozzle interval C is larger than that of
combinations of the nozzles having the nozzle interval B.
Consequently, an area printed by nozzles located in the joint c and
the vicinity of the joint c, the number of dots having the dot
interval C' is larger than that of dots having the dot interval B'.
The area printed by nozzles located in the joint c and the vicinity
of the joint c is thus perceived as a black stripe. As described
above, tilted joint head may result in a white or black stripe in
the area printed by joints of the print head, degrading the quality
of recorded images.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an ink jet
printing apparatus and an ink jet printing method which can prevent
possible stripe-like density unevenness in a joint in a print head
constructed by joining a plurality of chips together even if the
print head is inclined to the regular position of the print
head.
To achieve this object, the present invention is configured as
described below.
A first aspect of the present invention is an ink jet printing
apparatus performing printing by moving a print head having a
plurality of nozzle arrays each including a plurality of the
nozzles through which ink is ejected, relative to a print medium
while ejecting ink to the print medium through the nozzles, the
nozzle arrays being shifted in a direction in which the nozzles are
arranged, so as to have overlapping portions in a direction
orthogonal to the nozzle arranging direction, the apparatus
comprising: a controller that controls an ink ejecting operation of
the nozzles in the overlapping portions on the basis of an angle
between a direction in which the plurality of nozzle arrays are
arranged and a reference direction orthogonal to the direction in
which the print head moves relative to the print medium.
A second aspect of the present invention is an ink jet printing
apparatus performing printing by moving a print head having a
plurality of nozzle arrays each including a plurality of the
nozzles through which ink is ejected, relative to a print medium
while ejecting ink to the print medium through the nozzles, the
nozzle arrays being shifted in a direction in which the nozzles are
arranged, so that positions of ends of the nozzle arrays adjacent
to each other in the nozzle arranging direction are equal in the
nozzle arranging direction, the apparatus comprising: a controller
that controls an ink ejecting operation of nozzles located at ends
of the plurality of nozzle arrays on the basis of an angle between
a direction orthogonal to the moving direction of the print head
relative to the print medium and a direction in which the plurality
of nozzle arrays are arranged.
A third aspect of the present invention is an ink jet printing
method of performing printing by moving a print head having a
plurality of nozzle arrays each including a plurality of the
nozzles through which ink is ejected, relative to a print medium
while ejecting ink to the print medium through the nozzles, the
nozzle arrays being shifted in a direction in which the nozzles are
arranged, so as to have overlapping portions in a direction
orthogonal to the nozzle arranging direction, the method
comprising: a measuring step of measuring an angle between a
direction orthogonal to the direction in which the print head moves
relative to the print medium and a direction in which the plurality
of nozzle arrays are arranged; and a control step of controlling an
ink ejecting operation of the nozzles in the overlapping portions
on the basis of the angle measured in the measuring step.
The term "print" as used herein refers not only to formation of
significant information such as letters or graphics but also to
formation of images, patterns, or the like on a printed material or
processing of a print medium, in a broad sense, regardless of
whether or not the image is significant and whether or not the
image is actualized so as to be visually perceived by human
beings.
The term "print medium" refers not only to paper used for common
ink jet printing apparatuses but also to clothes, plastic films,
metal plates, or the like, that is, anything that can receive ink
ejected by a head, in a broad sense.
The term "ink" should be broadly interpreted as in the case of the
definition of the term "print" and refers to a liquid applied onto
a printed material and used to form images, patterns, or the like
or to process a printed material.
Even if the print head is inclined to the appropriate position
thereof, the present invention can prevent possible stripe-like
density unevenness that may occur at a joint between chips. This
enables high image quality to be achieved even with what is called
a joint head.
Further features of the present invention will become apparent from
the following description of exemplary embodiments (with reference
to the attached drawings).
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram schematically showing a print head (joint head)
used in an embodiment of the present invention;
FIG. 2 is an enlarged view schematically showing how chips are
joined together in a print head used in a first embodiment of the
present invention;
FIG. 3 is a diagram showing that the print head shown in FIG. 2 is
inclined as well as the resulting intervals between adjacent
nozzles in joints;
FIG. 4 is a perspective view conceptually showing an ink jet
printing apparatus to which the present invention is
applicable;
FIG. 5 is a partly cutaway perspective view showing the internal
configuration of a print head using electrothermal conversion
elements as ejection energy generating elements for ink
droplets;
FIG. 6 is a block diagram showing the circuit configuration of a
control system in the embodiment of the present invention;
FIG. 7A is a diagram showing a driving pulse used to drive
electrothermal conversion elements in a print head, and
specifically, showing a single pulse;
FIG. 7B is a diagram showing a driving pulse used to drive the
electrothermal conversion elements in the print head, and
specifically, showing a double pulse;
FIG. 8 is a diagram showing 2-bit selection data allowing the
selection of a driving pulse (double pulse) corresponding to each
of the nozzles in the print head;
FIGS. 9A to 9I are waveform diagrams showing pre-pulses and a main
pulse selected in accordance with the selection data and synthesis
waveforms of double pulses obtained by synthesizing the pre-pulses
and the main pulse;
FIG. 10 is a circuit diagram showing a part of the configuration of
a driving circuit for the print head used in the first embodiment
of the present invention;
FIG. 11 is a diagram illustrating a joint between chips CH (N-1)
and CN (N) in a print head in accordance with a second embodiment
as well as the usage rate of nozzles positioned in the joint,
wherein the print head is located in a regular position;
FIG. 12 is a diagram illustrating the joint between the chips CH
(N-1) and CN (N) in the print head in accordance with the second
embodiment as well as the usage rate of the nozzles positioned in
the joint, wherein the print head is inclined to the regular
position;
FIG. 13 is a diagram illustrating the joint between chips CH (N)
and CN (N+1) in the print head in accordance with the second
embodiment as well as the usage rate of the nozzles positioned in
the joint, wherein the print head is inclined to the regular
position;
FIG. 14 is a diagram illustrating a joint between chips CH (N) and
CN (N+1) in a print head in accordance with a third embodiment as
well as the usage rate of nozzles positioned in the joint;
FIG. 15 is a diagram showing an example of the configuration of
nozzle chips in a print head used in a fourth embodiment of the
present invention;
FIG. 16 is a diagram illustrating joints in a print head used in a
fifth embodiment of the present invention and the interval between
adjacent nozzles in each of the joints, wherein the print head is
inclined to the regular position thereof;
FIG. 17 is a diagram showing a pattern used for measurement of the
inclination of the print head in the embodiment of the present
invention;
FIG. 18 is a diagram showing a pattern forming method used for
measurement of the inclination of the print head in the embodiment
of the present invention;
FIG. 19A is a diagram showing a joint b including combinations of
nozzles having a nozzle interval B shown in FIG. 3 and combinations
of nozzles having a nozzle interval C shown in FIG. 3;
FIG. 19B is a diagram showing an example of arrangement of dots
printed by nozzles arranged in the joint b and the vicinity of the
joint b when a print head H is tilted;
FIG. 19C is a diagram showing another example of arrangement of
dots printed using the nozzles arranged in the joint b and the
vicinity of the joint b;
FIG. 20A is a diagram showing a joint c including combinations of
the nozzles having the nozzle interval B, shown in FIG. 3, and
combinations of the nozzles having the nozzle interval C, shown in
FIG. 3;
FIGS. 20B and 20C are diagrams showing the arrangement of dots
printed by the nozzles arranged in the joint c and the vicinity of
the joint c when the print head H is tilted, wherein black circles
show dots printed by nozzles in a chip CH(N) and white circles show
dots printed by nozzles in a chip CH(N+1); and
FIG. 21 is a diagram schematically showing a print head having
chips arranged like steps.
DESCRIPTION OF THE EMBODIMENTS
Embodiments of the present invention will be described below in
detail with reference to the drawings.
First Embodiment
FIG. 4 is a perspective view schematically showing a full line ink
jet printing apparatus (hereinafter simply referred to as a
printing apparatus) in accordance with an embodiment of the present
invention.
An ink jet printing apparatus 1 shown in FIG. 4 is what is called a
full line type having elongate print heads (hereinafter referred to
as "joint heads") for respective ink colors each of which is
constructed by joining a plurality of chips such as those shown in
FIG. 1. In FIG. 4 shows that four print heads H eject four color
inks, yellow (YE) ink, magenta (M) ink, cyan (C) ink, and black
(Bk) ink, respectively, to form an image. However, the present
invention is not limited to the types of the inks used, the number
of print heads, and the like shown in FIG. 4. These factors can be
optionally set and the present invention is effective in any
case.
The full-line printing apparatus performs a printing operation by
conveying a print medium along a direction substantially orthogonal
to the longitudinal direction of the print heads H. Each of the
print heads H has a print width equal to or greater than the width
of the maximum available print medium. Furthermore, the print
medium M is conveyed by cyclically moving an endless conveying belt
VL by means of a motor (not shown) in accordance with the present
invention. An image is formed on the print medium by ejecting ink
droplets from the print heads H in accordance with print data while
moving the conveying belt VL to continuously convey the print
medium M placed on a top surface of the conveying belt VL.
Now, with reference to FIG. 5, a brief description will be given of
the internal structure of the print head applied to the present
embodiment.
The print head H shown in FIG. 5 is an ink jet print head in which
ink is rapidly heated by an electrothermal conversion element
(heater) to generate bubbles so that the pressure of the bubbles
causes ink droplets to be ejected from ejection orifices.
The print head H comprises a heater board 104 that is a board on
which a plurality of heaters 102 that heat ink and a top panel 106
placed on the heater board 104. A plurality of ejection orifices
108 are formed in the top panel 106. Tunnel-like liquid path liquid
paths 110 are formed behind the respective ejection orifices 108 so
as to be in communication with the ejection orifices 108. Each of
the liquid paths 110 is isolated from the adjacent liquid paths by
bulkheads 112. All the liquid paths 110 are connected to one ink
liquid chamber 114 located behind the liquid paths 110. Ink is
supplied to the ink liquid chamber 114 via an ink supply port 116.
The ink is fed from the ink liquid chamber 114 to the respective
liquid paths 110.
The heater board 104 and the top panel 106 are aligned and
assembled together so that the heaters 102 are positioned in
association with the respective liquid paths 110. FIG. 5 shows only
two heaters 102. However, in actuality, the heaters 102 and the
liquid paths 110 are provided on a one-to-one basis. The heater
board 104 is manufactured by a semiconductor process using a
silicon substrate as a base. Signal lines that drive the heaters
102 are connected to a driving circuit formed on the same board.
Supplying a predetermined driving pulse to the heaters 102 causes
the ink on the heaters 102 to be boiled to form bubbles. The
bubbles expand to increase the volume thereof to eject the ink from
the ejection orifices 108. This is the principle of ink ejection in
the ink jet print head using the electrothermal conversion
elements. In the present specification and claims, an ink ejecting
section (nozzles) means apart including the ejection orifices 108,
the liquid paths 110, and the heaters 102.
FIG. 6 is a block diagram showing the general configuration of a
control system in the ink jet printing apparatus in which the
embodiment of the present invention is mounted.
In FIG. 6, reference numeral 801 denotes a CPU that executes
various calculations, determinations, and control processes. The
CPU 801 controls the whole printing apparatus in accordance with
software programs and the like stored in a ROM 802. Reference
numeral 803 denotes a conveying section that conveys print media
such as print sheets or OHP films and that corresponds to the
conveying belt and a motor driving the conveying belt. Reference
numeral 804 denotes an ejection recovery section that performs an
operation of recovering the ejection performance of the print head.
Reference numeral 807 denotes a driving circuit that controls
ejections from the print head. Reference 808 denotes a binarization
circuit that converts an image to be printed into ejection data and
that executes a halftone process and the like on image data.
Reference numeral 809 denotes an image processing section that
executes image processing such that in this case, if the image to
be printed is a color image, input image data is separated into ink
colors used for the printing apparatus. Reference numeral 810
denotes a RAM that stores data required to control ejections as
described below. The RAM 809, the CPU 801, the ROM 802, and the
driving circuit 806 constitute control means in accordance with the
present invention.
Reference numeral 811 denotes a head inclination detecting section
(detecting means) that detects the inclination of the print head H,
that is, the inclination (angle) of a direction in which the print
head H performs a scan operation relative to a print medium (with a
full line head, a direction in which the print medium is conveyed),
to the reference direction, which is orthogonal to the print medium
conveying direction. The detecting means is composed of an optical
sensor such as a CCD which optically reads an inclination detecting
pattern printed on the print medium as described below. Data
obtained by reading the inclination detecting pattern is sent to
the CPU 801. The CPU 801 determines the inclination of the print
head on the basis of the data read by the head inclination
detecting section 811 and reads data required for ejection control
from the RAM as required. The head inclination detecting section
811 and the CPU 801 constitute measuring means in accordance with
the present invention.
Now, on the basis of the above-described configuration, description
will be given of the ink ejection control performed by the ink jet
printing apparatus in accordance with the present embodiment.
In the present embodiment, before starting the use of the ink jet
printing apparatus, the print head H is used to print a pattern
(measuring pattern) required to measure the inclination of the
print head H, on the print medium. The inclination of the print
head H is then measured on the basis of the pattern.
FIG. 17 shows an example of the measuring pattern required to
measure the degree (angle) of the inclination of the print head H.
FIG. 18 shows a method for printing the measuring pattern P. As
shown in FIGS. 17 and 18, the measuring pattern P is divided into
two patterns, an upper pattern P1 and a lower pattern P2. The two
patterns P1 and P2 are printed on the print medium M in two
separate steps, using the print medium H constructed by joining the
four short chips CH1 to CH4 together. That is, first, the upper
pattern P1 in FIG. 17 is printed, and then the print head H or the
print medium M is relatively shifted in the vertical direction. The
pattern P2 is then printed.
The pattern P1, printed in the first printing operation, includes a
plurality of (in the figure, 15) linear patterns (lines) P11
extending in the vertical direction, numbers P12 printed above the
respective lines P11, and a pattern P13 used to check how each of
the nozzles in the print head ejects ink. The numbered lines P11
are formed at fixed intervals (in this case, an integral multiple
of printing resolution). The numbered linear patterns P11 are
printed by the chip CH4, one of the four chips of the print head H
which is located at the lowermost end in the figure.
On the other hand, the pattern P2, printed in the second printing
operation, includes a plurality of (15) linear patterns P21
extending in the vertical direction and printed at fixed intervals,
similarly to the linear patterns P11, printed in the first printing
operation. A pattern P23 is also printed to allow ejection
performance to be checked. In this case, the pattern P2 is printed
by the chip CH1, one of the four chips of the print head H which is
located at the uppermost end in the figure.
The inclination of the print head can be measured on the basis of
the pattern P printed as described above. That is, if the
inclination of the print head is zero, the 0th line (line no. 0) in
the upper lines P11 overlaps the 0th line (the line positioned in
the center (and longer than the other lines)) P21a in the lower
lines P21. However, if the print head H is inclined, the lower
center line P21a shifts from the upper 0th line and overlaps
another line, depending on the inclination. On the basis of the
amount of shift of the lower line P21a from the 0th line and the
total length (L) of the upper pattern P1, the inclination of the
print head H can be determined in accordance with the following
formula. That is, on the basis of the shift amount and the total
length of the upper pattern, the inclination (.theta.) of the head
can be determined in accordance with the following formula.
Sin(.theta.)=(shift amount)/(total length of the upper pattern
P1)
Whether the shift amount is present on the right or left side of
the 0th line determines the direction of the inclination of the
whole print head H. If the inclining direction is reversed, the
ejection control method executed on the joints b and c between the
chips needs to be exactly reversed. For example, as shown in FIG.
3, if the print head is located so as to be high on the right with
respect to the appropriate arranging direction, in the joint b, the
number of combinations of nozzles having an increased adjacent
nozzle interval increases, whereas in the joint c, the number of
combinations of nozzles having a reduced adjacent nozzle interval
increases. That is, white stripes are likely to occur at the joint
b, whereas black stripes are likely to occur at the joint c. In
contrast, if the print head is located so as to be low on the right
with respect to the appropriate arranging direction, in the joint
b, the number of combinations of nozzles having a reduce nozzle
interval between the adjacent nozzles increases, whereas in the
joint c, the number of combinations of nozzles having an increased
adjacent nozzle interval increases. That is, black stripes are
likely to occur at the joint b, whereas white stripes are likely to
occur at the joint c.
Thus, whether white or black stripes occur depends on the degree of
the inclination of the print head H. Consequently, the present
embodiment controls the ejecting operation of the nozzles in the
joint on the basis of the angle .theta. of the inclination of the
print head H and the direction of the inclination of the print head
H.
A specific description will be given of the control of the ejecting
operation of the print head performed in accordance with the
present embodiment.
To prevent possible white and black stripes in a print area
corresponding to the nozzles in the joint, the present embodiment
controls the ink amount of ejected ink droplets. The ink amount of
ejected ink droplets is controlled by varying the application
voltage or time of a driving signal supplied to the driving circuit
807.
As already described, the print head H rapidly heats ink by the
heaters 102 to generate bubbles in the ink. The bubbles expand to
increase the volume thereof to push the ink from the ejection
orifices. Thus, the size of the bubbles can be adjusted by
controlling a driving pulse applied to the heaters 102. This in
turn makes it possible to control the amount of ink ejected during
a single ink ejecting operation, that is, the ink amount of ink
droplets (hereinafter also referred to as the ejection amount).
FIGS. 7A and 7B illustrate a driving pulse for the heaters. FIG. 7A
shows the pulse waveform of single pulse driving. FIG. 7B shows the
pulse waveform of double pulse driving. With the single pulse
driving in FIG. 7A, the ink amount of ink droplets can be
controlled by varying pulse width T instead of a voltage (V-V0).
Furthermore, in connection with the control range of the ejection
amount, the double pulse driving in FIG. 7B allows the ejection
amount to be adjusted over a wider range than the single pulse
driving and is thus a more effective control scheme. That is, most
of the heat generated by the heaters is absorbed by the ink
contacting the surface of the heaters. Accordingly, application of
a pre-pulse enables the ink itself to be sufficiently heated to
help the subsequent ejection of ink droplets caused by the main
pulse. Thus, the double pulse driving allows the ejection amount to
be controlled more efficiently than the single pulse driving.
In FIGS. 7A and 7B, when T1, T2, and T3 denote pre-pulse width,
halt period, and main pulse width, respectively, and the main pulse
width T3 is fixed, varying the pre-pulse width T1 enables the
ejection amount of the nozzles in each of the joints in the print
head H. That is, increasing T1 increases the ejection amount,
whereas reducing T1 reduces the ejection amount.
Now, an example of the double pulse driving will be shown in which
the ejection amount is controlled by assigning the different
pre-pulses T1 to the respective nozzles.
As shown in FIG. 8, 2-bit data corresponding to the nozzles is
written in RAM areas A and B (corresponding to the ejection control
data RAM 810). Specifying the 2-bit data enables selection from
pulses PH1 to PH4 of respective pulse widths shown in FIGS. 9A to
9D.
For example, if bit data input to nozzles b1 and b2 (see FIG. 3)
corresponding to a joint is (0, 1), the pulse PH2 is selected. If
bit data input to nozzles c1 and c2 (see FIG. 3) is (1, 0), the
pulse PH3 is selected.
Thus, assigning bit data for pre-pulse selection to the respective
nozzles enables the ejection amount of each nozzle to be varied.
After the pre-pulse is applied to the heaters, a main pulse MH
shown in FIG. 9E is applied.
FIG. 10 shows the configuration of a driving circuit for the
heaters.
In FIG. 10, reference character VH denotes a power voltage for the
ink jet head, and reference numeral H.sub.GND denotes ground for
VH. Reference character MH denotes the main pulse, and reference
characters PH1 to PH4 denote the pre-pulses. Reference character
B.sub.LAT denotes a bit latch signal instructing the bit data
(selection bit data) for selection from PH1 to PH4 to be latched.
DLAT denotes a data latch signal that causes data (print data)
required for printing to be latched. Reference character DATA
denotes bit data and print data transferred to a shift register as
serial data.
In the driving circuit configured as described above, the bit data
shown in FIG. 8 is transferred through a DATA signal line to a
shift register 301 as serial data. Once the bit data on all the
nozzles is transferred to the shift register 301, a bit latch
signal B.sub.LAT is generated to latch the bit data.
The print data DATA, required for printing, is then transferred to
the shift register 301 through the DATA signal line, similarly to
the bit data (selection bit data). Once the print data for all the
nozzles is transferred, the data latch signal D.sub.LAT is
generated to cause a data latch circuit 302 to latch print data.
Then, on the basis of the bit data already latched by the bit latch
circuit 303, a selection logic circuit 304 selects one of PH1 to
PH4. The selected one of the pre-pulses PH1 to PH4 and the main
pulse MH are synthesized by an OR circuit 305. The logical AND of
an output from the OR circuit 305 and the print data is then output
by an AND circuit 306 as a driving signal (electric signal). The
driving signal is input to a base of a transistor 307 for each of
the nozzles. If the driving signal input to the base of the
transistor 307 is an ON signal, the transistor is turned on. The
power voltage VH allows current to flow through a resistor 308
(corresponding to the heater), which thus generates heat. The heat
generates bubbles in the ink in the nozzle to eject the ink. This
operation is performed on all the nozzles.
FIGS. 9F to 9I show the waveforms of synthetic signals of the heat
pulse signal PH and the main pulse signal MH output by the OR
circuit 305. As shown in the figures, the synthetic signals are
obtained by synthesizing the fixed main pulse MH with the pulse
signals of different pulse widths. To change the ink ejection
amount, the bit data DATA corresponding to the required ejection
amount is sent to the shift register 301, and the bit latch signal
B.sub.LAT is generated, at the timing of the change. This enables
the ink amount of ink droplets ejected from the nozzles
corresponding to new bit data.
Now, description will be given of the control of the ejection
amount for the joint in the print head H in accordance with the
present embodiment, in accordance with a control procedure.
First, the head inclination detecting section 811, shown in FIG. 6,
measures the inclination of each chip using the method described
with reference to FIGS. 17 and 18. On the basis of the degree
(angle) of the measured inclination, the CPU 801 varies the
ejection amounts of the nozzles b1 and b2 as well as c1 and c2,
forming the intervals B and C, respectively. If the print head is
inclined so as to be high on the right as shown in FIG. 3, then as
shown in the above calculation, the interval B between the nozzles
b1 and b2 in the S direction is greater than the inter-nozzle
distance R depending on the degree (angle) of the inclination.
Consequently, white stripes may occur in an area printed by the
nozzles b1 and b2, having the nozzle interval B, and nozzles
combined in the same manner as that in which the nozzles b1 and b2
are combined. The CPU 801 thus controllably increases the ejection
amount of the nozzles having the nozzle interval B. That is, the
CPU 801 sends bit data to the driving circuit such that a wider
pre-pulse is selected from those shown in FIGS. 9F to 9I.
On the other hand, the interval C between the nozzles c1 and c2 in
the S direction is smaller than the inter-nozzle distance R.
Therefore, an area printed by the nozzles c1 and c2, having the
nozzle interval C, and nozzles combined in the same manner as that
in which the nozzles c1 and c2 are combined may occur black
stripes. Thus, as opposed to the above case, the CPU 801
controllably reduces the ejection amount of the nozzles having the
nozzle interval C. In either case, experiments and examinations are
performed to predetermine by what amount the ejection amount is to
be increased or reduced depending on the inclination of the print
head, that is, an increase or decrease in nozzle interval. The data
obtained is stored in the "ejection amount correction data RAM" 810
in FIG. 8 so that the driving pulses for the nozzles having the
nozzle intervals B and C are determined on the basis of the
measured inclinations. This enables the ejection amount to be
appropriately controlled in accordance with the inclination of the
print head, allowing a reduction in the occurrence of white or
black stripes in print images. Alternatively, the occurrence of a
white or black stripe in a printed image can be reduced by
controlling the ejection amounts of all the nozzles in the
joint.
The present embodiment uses the 2-bit selection bit data to select
one of the four pre-pulses. Increasing the number of bits in the
selection bit data enables the ejection amount to be more precisely
controlled. However, this complicates the configuration of the
circuit and increases costs. Therefore the variable range of the
required ejection amount is determined by previously examining to
what degree the inclination of the print head can be reduced on the
basis of the specification (for example, mechanical measures) of
the whole apparatus.
Furthermore, in the first embodiment, with the voltage of the
driving pulse fixed, and the pulse width is switched to vary the
ejection amount. However, similar effects can be exerted by varying
the voltage of the pulse with the pulse width of the driving pulse
fixed. Moreover, control can be performed by varying both the pulse
width and voltage of the driving pulse. This enables more precise
control.
Second Embodiment
Now, a second embodiment of the present invention will be
described.
The first embodiment controls the amount (ejection amount) of ink
droplets ejected from the nozzles positioned in each of the joints
in the print head H. In contrast, the second embodiment reduces the
occurrence of white and black stripes in an area printed by the
nozzles positioned in the joint by controlling the number of ink
droplets ejected from the joint in accordance with the inclination
of the print head H. An ink jet printing apparatus in accordance
with the second embodiment is of a full-line type using what is
called a joint head composed of a plurality of combined chips and
having a configuration shown in FIGS. 4 to 10 as is the case with
the first embodiment.
In the print head H used in the second embodiment, joined ends
overlap each other as is the case with the first embodiment. FIG.
11 shows the arrangement of dots formed by the nozzles positioned
in that area (joint) b of the print head H in accordance with the
second embodiment in which the chips CH1 and CH2 overlap.
FIG. 11 shows that the print head H is appropriately located, that
is, the print head H is not inclined. In this case, as shown in the
figure, those parts of the chips CH1 and CH2 which are positioned
in the joint b are each responsible for printing at a nozzle usage
rate of 50%. In this case, the chips CH1 and CH2 alternately eject
ink to provide an amount of ink required for forming an image
(100%).
On the other hand, in a non-joint portion a of each of the chips
CH1 and CH2, only one nozzle is used to form a print image. That
is, the nozzle usage rate of the non-joint portion a is 100%. The
term "nozzle usage rate" as used herein means the rate at which the
nozzle ejects ink for a print image for which the nozzle is
responsible. In other words, the nozzle usage rate means the ratio
(ejection data/print data) of print data made up of data (ejection
data) instructing the nozzle to eject ink and data (non-ejection
data) instructing the nozzle not to eject ink to data instructing
an ink ejecting operation to be performed.
Now, description will be given of nozzle ejection control performed
on the joints (overlapping portions) b between the chips CH (N-1)
and CH (N) and between the chips CH (N) and CH (N+1) on the
assumption that the print head H is inclined so as to be high on
the right as shown in FIG. 3.
As already described, in the joint b between the chips CH (N-1) and
CH (N), the number of nozzle combinations in which the interval
between the adjacent nozzles is greater than the inter-nozzle
distance R increases. As a result, white stripes may occur. Thus,
control is performed such that the nozzle usage rate of the joint b
is increased to increase the number of ink droplets ejected from
the joint b between the chips CH (N-1) and CH (N) as shown in FIG.
12. In FIG. 12, both the chips CHIN) and CH (N-1) have a nozzle
usage rate of 75% in the joint b. This corresponds to a 25%
increase in nozzle usage rate in the joint b in each chip compared
to the nozzle usage rate used when the print head H is not
inclined. That is, the total usage rate of the nozzles positioned
in the joint b in both chips is 150%. This increases the number of
nozzles positioned in the nozzle b, reducing the occurrence of
white stripes.
In FIG. 12, the nozzle usage rates of the chips CH (N) and CH (N-1)
in the joint b are set at the same value. However, similar effects
can be exerted by setting the nozzle usage rates of the chips CH
(N) and CH (N-1) at different values. That is, the white stripe
inhibiting effect can also be exerted by increasing the total usage
rate of the chips CH (N) and CH (N-1) in the joint b. For example,
the usage rate of one of the chips CH (N) and CH (N-1) may be
increased or the usage rates of the nozzles positioned in the joint
b in each chip may be set at different values. This enables
possible white stripes to be inhibited.
On the other hand, in the joint b between the chips CH (N) and CH
(N+1), the number of nozzle combinations in which the interval
between the adjacent nozzles is smaller than the inter-nozzle
distance R increases. Thus, control is performed so as to reduce
the nozzle usage rate of the nozzles in the joint b between the
chips CH (N) and CH (N+1). In FIG. 13, control is performed so as
to set the total of the usage rates of the chips CH (N) and CH
(N+1) at 75%. That is, the total of the usage rates of the nozzles
in the joint b in the chips is reduced by 25% compared to the total
of the usage rates of the chips in the joint b used when the print
head H is not inclined. In this case, the total of the usage rates
of both chips in the joint b can be reduced in various combinatory
manners. For example, the nozzle usage rates of both chips may be
reduced or the nozzle usage rate of only one of the chips may be
reduced. In FIG. 13, one of the chips CH (N) and CH (N+1) is set at
a usage rate of 25%. Possible black stripes can be inhibited by
thus reducing the total of the nozzle usage rates of both chips CH
(N) and CH (N+1) compared to the nozzle usage rates used when the
print head H is not inclined.
The above-described ink droplet ejection control is performed by
first detecting the inclination of the print head H, and based on
the result of the detection, changing the nozzle usage rate for the
joint b and thus the number of ink droplets ejected from the
nozzles, as is the case with the first embodiment. More
specifically, on the basis of the inclination of the print head H,
the CPU 801, shown in FIG. 6, reads correction data from the
ejection control data RAM 810. On the basis of the correction data,
a correction process is executed on initial print data obtained
when the print head H is not inclined. That is, a correction
process of increasing or reducing the number of ejected ink
droplets is executed on that part of the initial print data
supplied to each of the chips which corresponds to the joint.
Experiments may be conducted to pre-obtain data on the basic
characteristics of the print head H relating to the inclination and
nozzle usage rate thereof, that is, ejection control data
indicating by what amount the nozzle usage rate is to be changed in
accordance with the inclination of the print head H. The data
obtained is stored in the ejection control data RAM 810 to allow
the above-described ejection control to be performed.
Third Embodiment
In the description of the second embodiment, control is performed
such that the nozzle usage rate of the nozzles positioned in each
joint is uniform within the same chip by way of example. In
contrast, a third embodiment of the present invention not only
performs the ejection control of the joint against the inclination
of the print head but also performs control such that the usage
rate of the nozzles in the joint in each chip decreases
consistently with the distance between the nozzles and the end of
the chip as shown in FIG. 14.
In general, in the inkjet print head, the nozzles located closer to
the end of the chip tend to exhibit lower ejection performance
(ejection direction or amount). Thus, performing control such that
the ink ejection rate is reduced for the nozzles located closer to
the end of the chip is conventionally known to be effective for
inhibiting possible density unevenness (for example, black and
white stripes) at the joint.
Thus, in the third embodiment, in performing control such that the
ink ejection rate is reduced for the nozzles located closer to the
end of the chip, the usage rate of the nozzles positioned in the
joint in each chip is corrected on the basis of the inclination of
the print head H as is the case with the second embodiment. Of
course, in this case, since the print data used when the print head
H is located in the regular position is different from that in the
second embodiment, the correction data on the nozzle usage rate,
which is to be varied depending on the inclination of the print
head, needs to be set at values different from those in the second
embodiment. Thus, also in the third embodiment, experiments or
pre-examinations are performed to determine the appropriate
correction amount for the number of ink ejections in association
with the inclination of the print head. The data corresponding to
the correction amount is stored in the ejection correction data RAM
in FIG. 6. This enables the conventional end control to be combined
with the control of the number of ejected ink droplets against the
inclination of the print head in accordance with the present
invention. Possible density unevenness can thus be more effectively
inhibited.
Fourth Embodiment
In the above description of the embodiments, one nozzle array is
provided in each of the chips provided in the print head H by way
of example. However, the present invention is applicable to an ink
jet printing apparatus that performs a printing operation using a
print head constructed by joining a plurality of chips each having
a plurality of nozzle arrays. A print head H1 shown in FIG. 15 has
a plurality of nozzles staggered in each of the chips CH (N-1) and
CH (N) so as to form two nozzle arrays. The print head H1 can thus
form dense dots.
If the print head constructed by thus joining the chips each having
the plurality of nozzle arrays is inclined to the regular position
thereof, stripe-like density unevenness such as white or black
stripes may also occur in the joint in each chip. Therefore, the
present invention is effective on this print head. In this case, it
is essential that a plurality of nozzles overlap in the joint.
Fifth Embodiment
In the above description of the embodiments, the print head is used
in which the nozzles positioned near the end of one of the chips
overlap the nozzles positioned near the end of the other chip, by
way of example. However, the present invention is also applicable
to an ink jet printing apparatus using a print head in which the
end nozzles in one of the chips do not overlap the end nozzles in
the other chip.
FIG. 16 shows that a print head H2 is located so as to be high on
the right, that is, inclined at an angle .theta. to the direction
(reference direction) S orthogonal to the direction in which the
print head H performs a scan operation relative to the print medium
(with a full line head, the direction in which the print medium is
conveyed). In this case, in each of the joints b of the print head
H2, the number of combinations of nozzles having the adjacent
nozzle interval B increases. In the joint c, the number of
combinations of nozzles having the adjacent nozzle interval C
increases. Thus, unless the print data is corrected, white stripes
may occur in the joint b, while black stripes may occur in the
joint c. To avoid this, control is performed so as to increase the
usage rate of the nozzles positioned in the joint b in the print
head H2, while reducing the usage rate of the nozzles positioned in
the joint c in the print head H2. This enables a reduction in the
occurrence of striped-like density unevenness at the joints b and
c. However, since the nozzles in the joint in one of the chips of
the print head H2 do not overlap the nozzles in the joint in the
other chip, the density unevenness inhibiting effect may not be
exerted under specific conditions. That is, if an image is printed
at a very high printing rate (printing duty) of, for example, 100%,
it is impossible to print the image at a printing rate exceeding
100% using one nozzle that does not overlap any other nozzle. Thus,
if white stripes occur, the printing rate, at which the image is
formed, cannot further be increased, possibly preventing sufficient
corrections. However, the control in accordance with the present
embodiment is effective unless an image is formed at an extreme
printing rate as described above. Furthermore, even if an image is
formed at a high printing rate, it is possible to reduce the
occurrence of density unevenness (white stripes) at the high
printing rate by performing a combination of several types of
ejection amount control as in the case of the first embodiment.
Other Embodiments
In the above-described embodiments, the print head inclination
detecting section 801 is provided in the ink jet printing
apparatus. However, the inclination of the print head may be
measured, for example, before shipment from a factory, and
correction data based on the measurement may be stored in the RAM
810. This eliminates the need to mount hardware for detecting the
inclination of the print head, on the ink jet printing apparatus.
This in turn makes it possible to avoid increasing apparatus costs.
However, in this case, the inclination of the print head needs to
be prevented from varying over time, or even if the inclination
varies, the variation needs to fall within an allowable range.
Therefore, in the most desirable form, the head inclination
detecting section 811 is provided, and the inclination data on the
print head measured before shipment from the factory is held in the
RAM. That is, in the desirable form, initially, on the basis of the
inclination data measured before shipment from the factory, any of
the correction data in the RAM is selected to determine the
correction amount for the joint. Subsequently, the inclination of
the head is periodically measured to change the correction amount
data in the RAM as required.
Furthermore, the present invention is not limited to the full line
ink jet printing apparatus but is applicable to a serial ink jet
printing apparatus that performs a main scanning operation of
moving the print head in the direction orthogonal to the print
medium conveying direction and an operation of conveying the print
medium (a sub-scanning operation). That is, a serial ink jet
printing apparatus may use a print head composed of a plurality of
short chips joined together and may perform a printing operation by
moving the print head in a main scanning direction. In this case,
effects similar to those of the above-described embodiments are
expected to be produced even if the print head is tilted in the
direction orthogonal to the main scanning direction (the direction
in which the print head H performs a scan operation relative to the
print medium), in which the print head is moved. The present
invention is also applicable to an ink jet printing apparatus that
moves the print head with the print medium fixed in order to move
the print medium and the print head relative to each other.
The embodiments have been described taking, as an example, the use
of what is called a joint head having an increased length as a
result of the arrangement in which chips are sequentially joined
together. However, the present invention is applicable to a print
head that is not composed of a plurality of chips. For example, the
present invention is expected to exert similar effects on a print
head composed of one chip but having nozzle arrays each including a
plurality of nozzles and arranged so as to be sequentially joined
together.
Furthermore, the arrangement of the chips in the print head is not
limited to the staggered one. A configuration may also be used in
which the chips are arranged like steps as shown in FIG. 21. In
this case, a tilt of the print head results in one of a black
stripe and a white stripe in all the joints.
The above-described embodiments use the print head that uses heat
energy from the electrothermal conversion elements provided in the
nozzles to eject the ink from the ejection orifices. However, the
present invention is applicable to a print head using ejection
energy generating elements other than the electrothermal conversion
elements. For example, the present invention is applicable to a
print head using electromechanical conversion elements such as
piezoelectric elements as ejection energy generating elements.
While the present invention has been described with reference to
exemplary embodiments, it is to be understood that the invention is
not limited to the disclosed exemplary embodiments. The scope of
the following claims is to be accorded the broadest interpretation
so as to encompass all such modifications and equivalent structures
and functions.
This application claims the benefit of Japanese Patent Application
No. 2007-033650, filed Feb. 14, 2007, which is hereby incorporated
by reference herein in its entirety.
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